Power-Save for Wireless Networks

1. A power-save method implemented at a node in a wireless network having a shared communication medium, comprising: (a) determining whether a power-save trigger condition is satisfied, wherein the power-save trigger condition is a condition that, when satisfied, triggers entering a low power mode; (b) if the power-save trigger condition is satisfied, scheduling a CTS-to-self at a backoff time, wherein a destination address of the CTS-to-self matches an address of the node; (c) broadcasting the CTS-to-self at the backoff time; and (d) entering the low power mode following successful broadcast of the CTS-to-self.

2. The power-save method of claim 1 , wherein step (a) comprises determining whether a low level of network activity has been detected over the shared communication medium.

3. The power-save method of claim 1 , wherein step (a) comprises one or more of: determining whether a battery level at the node has dropped below a pre-determined battery level; and determining whether a time of the day condition is satisfied.

4. The power-save method of claim 1 , wherein the backoff time is calculated according to a uniform probability distribution function from the range [0, CW], where CW indicates a pre-determined contention window length.

5. The power-save method of claim 1 , wherein the broadcast CTS-to-self indicates an idle time duration following the broadcasting, and wherein the idle time duration is set such that the idle time duration does not straddle a scheduled beacon transmission required for network maintenance.

6. The power-save method of claim 1 , further comprising immediately before step (c): (e) determining if the node is the last broadcasting node of a network maintenance beacon; and (f) if the node is the last broadcasting node of the network maintenance beacon, omitting steps (c) and (d); wherein the network maintenance beacon is broadcast periodically by a random one of nodes in the network.

7. The power-save method of claim 1 , further comprising immediately before step (c): (e) determining if the shared communication medium is busy; and (f) if the shared communication medium is busy, omitting steps (c) and (d) and returning to step (b).

8. The power-save method of claim 1 , further comprising immediately before step (c): (e) determining if the shared communication medium is busy; (f) if the shared communication medium is busy, determining whether a current frame being transmitted over the shared communication medium is destined to the node; (g) if the current frame being transmitted over the shared communication medium is not destined to the node, omitting steps (c) and (d); and (h) entering the low power mode for at least a remaining transmission time of the current frame.

9. The power-save method of claim 1 , wherein step (d) comprises turning off a radio transceiver of the node for an idle time duration.

10. The power-save method of claim 1 , wherein step (c) comprises broadcasting the CTS-to-self at lower power than other transmissions over the shared communication medium.

11. The power-save method of claim 1 , wherein the broadcast CTS-to-self indicates an idle time duration following the broadcasting, and wherein the idle time is indicated in a network allocation vector (NAV) field of the CTS-to-self.

12. The power-save method of claim 1 , wherein the wireless network includes an Independent Basic Service Set (IBSS) network.

13. The power-save method of claim 1 , wherein the wireless network includes a Basic Service Set (BSS) network.

14. The power-save method of claim 1 , wherein the node includes a cellular phone.

15. The power-save method of claim 2 , wherein step (a) further comprises: monitoring network activity over a pre-determined number of consecutive beacon periods; generating a measure of network activity over the shared communication medium; and comparing the measure of network activity to a statistically generated measure of typical network activity of the shared communication medium.

16. The power-save method of claim 6 , wherein the network maintenance beacon is broadcast by the node when a beacon broadcast backoff time calculated by the node is minimum compared to beacon broadcast backoff times calculated respectively by other nodes in the wireless network, and wherein the beacon broadcast backoff time is calculated according to a uniform probability distribution function from the range [0, CW beacon ], where CW beacon indicates a pre-determined contention window length for beacon broadcast.

17. The power-save method of claim 8 , wherein step (h) comprises, depending on the remaining transmission time of the current frame, one of: turning off a radio transceiver, an oscillator, and a phase-locked loop (PLL) of the node; turning off only the radio transceiver of the node; and maintaining all radio components of the node turned on.

18. The power-save method of claim 16 , further comprising: increasing at least one of the beacon broadcast backoff time and the pre-determined contention window length for beacon broadcast, thereby decreasing a probability that the node will be the last broadcasting node of the network maintenance beacon in step (f).

19. The power-save method of claim 18 , wherein the backoff time is calculated according to a uniform probability distribution function from the range [0, CW], where CW indicates a pre-determined contention window length, further comprising: increasing at least one of the backoff time and the pre-determined contention window length, thereby increasing a probability that the shared communication medium will be busy at the random backoff time in step (f).

20. A computer program product comprising a non-transitory computer useable medium having computer program logic recorded thereon for causing a processor to implement a power-save method at a node in a wireless network having a shared communication medium, the power-save method comprising: determining whether a power-save trigger condition is satisfied, wherein the power-save trigger condition is a condition that, when satisfied, triggers entering a low power mode; scheduling a CTS-to-self at a backoff time when the power-save trigger condition is satisfied, wherein a destination address of the CTS-to-self matches an address of the node; broadcasting the CTS-to-self at the backoff time; and entering the low power mode following successful broadcast of the packet.

21. The computer program product of claim 20 , wherein determining whether the power-save condition is satisfied comprises determining whether a low level of network activity has been detected over the shared communication medium.

22. The computer program product of claim 20 , wherein the power-save method further comprises: determining if the node is the last broadcasting node of a network maintenance beacon; and cancelling the scheduled CTS-to-self if the node is the last broadcasting node of the network maintenance beacon, wherein the network maintenance beacon is broadcast periodically by a random one of nodes in the network.

23. The computer program product of claim 22 , wherein the network maintenance beacon is broadcast by the node when a beacon broadcast backoff time calculated by the node is minimum compared to beacon broadcast backoff times calculated respectively by other nodes in the wireless network, and wherein the beacon broadcast backoff time is calculated according to a uniform probability distribution function from the range [0, CW beacon ], where CW beacon indicates a pre-determined contention window length for beacon broadcast.

24. The computer program product of claim 20 , wherein the power-save method further comprises: determining if the shared communication medium is busy; and cancelling the scheduled CTS-to-self if the shared communication medium is busy.

25. The computer program product of claim 20 , wherein the power-save method further comprises: determining if the shared communication medium is busy; if the shared communication medium is busy, determining whether a current frame being transmitted over the shared communication medium is destined to the node; cancelling the scheduled CTS-to-self if the current frame being transmitted over the shared communication medium is not destined to the node; and entering the low power mode for at least a remaining transmission time of the current frame.

26. The computer program product of claim 20 , wherein the power-save method further comprises: turning off at least one of a radio transceiver, an oscillator, and a phase-locked loop (PLL) of the node.

27. The computer program product of claim 23 , wherein the power-save method further comprises: increasing at least one of the beacon broadcast backoff time and the pre-determined contention window length for beacon broadcast, thereby decreasing a probability that the node will be the last broadcasting node of the network maintenance beacon.

28. The computer program product of claim 24 , wherein the backoff time is calculated according to a uniform probability distribution function from the range [0, CW], where CW indicates a pre-determined contention window length, wherein the power-save method further comprises: increasing at least one of the backoff time and the pre-determined contention window length, thereby increasing a probability that the shared communication medium will be busy at the backoff time.